The invention relates to a method for manufacturing prepregs by impregnating reinforcement materials of glass, carbon or plastic in the form of fibers, nonwoven or woven fabrics or of paper-like materials with a cellulose base with a polyepoxy resin.
Composite materials with a base of a cross-linked, organic-polymer resin matrix and reinforcement materials or embedment components in the form of fibers, nonwoven and woven fabrics of glass, carbon or organic-synthetic material such as aramides (i.e., aromatic polyamides) or of paper-like materials with a cellulose base are of increased importance in various branches of engineering because they allow in a simple manner the combination of various particularly advantageous properties to form an advanced overall property picture. Of decisive importance here are the properties of the matrix material. Thus, the matrix material should have features which allow safe, reproducible processing as well as the far reaching utilization of the properties of the reinforcement materials or the embedment components.
A first feature is a matrix component which permits the manufacture of prepregs with sufficiently stable properties for further processing and which can be stored. For this purpose it is important that the prepregs should avoid adhesive character; however, they also should not be hardened completely; the resin matrix should only be prepolymerized, i.e., it still should be meltable. Features of the cross-linked resin matrix include high boundary surface adhesion with the reinforcement materials and embedment components and optionally, also with other materials, for instance, metallic or ceramic materials which are to be joined to fiber- or textile-reinforced prepregs. In the cross-linked condition, high chemical stability, dimensional stability under heat and (for electrical-engineering application) also durable, high electric insulation properties are further important features.
Such properties of a cross-linked polymer matrix can be achieved if aromatic and/or heterocyclic polyepoxy resins, i.e., polyglycidyl compounds are used and as a cross-linking component, i.e., as a hardener, aromatic polyamines. Examples for such polyamines are 4,4' diaminodiphenyl methane and 4,4'-diaminodiphenyl sulfone (see, for instance, DE-OS No. 32 10 746) and polyamines such as are known from German Pat. No. 27 43 680. The last-mentioned polyamines lead to particularly thermally dimensionally stable, aging-stable and non-inflammable network polymers. However, it has also been found that it is very difficult to maintain safe and reproducible processing techniques with cross-linking components of the kind mentioned above.
It is an object of the invention to develop a method for the manufacture of prepregs based on polyepoxy resins in such a manner that the manufacture of storage-stable prepregs is possible. It is an object also to manufacture composite materials from the prepregs which exhibit properties required of these materials.